On 22 Apr 2014, at 4:55pm, Dominique Devienne <ddevie...@gmail.com> wrote:
> Simply because of the extra space needed to store it. 36 bytes vs 16 > bytes. That's 20 wasted bytes for the PK, and everytime that PK is > references in other tables' FKs too. Times millions of rows, it adds > up, for nothing. The GUID is no less "genuine" as you put it, just > because it's stored as a 16-bytes blob rather than the canonical > 36-char text preferred by humans. And if you use GUIDs a lot, make two functions for SQLite which convert to and from text form. Loading external functions is something SQLite really is excellent at. On 22 Apr 2014, at 5:57pm, Stephan Beal <sgb...@googlemail.com> wrote: > http://www.w3.org/DesignIssues/Axioms.html#nonunique > > In summary: the context of a GUID defines its "scope of required > uniqueness," and a 16-byte GUID is essentially globally unique so long as > it has no collisions within its context(s). (i.e. who cares if SHA1s > collide, so long as it's not in the same repo?) You might be interested in UUIDs, which define the scope and provide methods for presenting hashed, sequential and random GUIDs within that scope: <http://en.wikipedia.org/wiki/Universally_unique_identifier> Libraries are available for many languages to generate UUIDs under many of these schemes. On 22 Apr 2014, at 6:57pm, RSmith <rsm...@rsweb.co.za> wrote: > Just to add - I cannot imagine why you would have dashes to start with Take, for example, this GUID: 550e8400-e29b-41d4-a716-44de5544ac00 A program (or a TABLE) frequently handles many GUIDs which differ only in one of the fields. For instance a program may have to represent a GUID externally (on the screen and output files) with the complete GUID, but it could store items internally (perhaps in a database) using only the last 12 hex digits, or as an integer up to 2^48. Since it know that all people GUIDs start 550e8400-e29b-41d4-a716- whereas all vehicles GUIDs start 550e8404-31e6-41d4-a716- there is no need to store them all in a table where the column tells you definitively whether you're talking about a person or a vehicle. When you're doing a lot of this sort of thing having the hyphens visible speeds up human time in figuring out what they're looking at. Simon. _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
